Because companies don’t actually give a shit about employee happiness? That’s my guess. I’m not saying this angrily, either. It’s business, all decisions are a means to an end.
I really like the idea, though. I would love to get an extra paycheck at the end of the year.
I think every company likes not having the liability of PTO hanging on the balance books, and most companies quietly enjoy the reduction in average PTO taken. For the outlier users of PTO, they'd better be firebreathers, or I suspect they are PIPed out.
BUT, we were in a somewhat competitive labor market up until very recently, and likely will be again some day. A generous PTO policy grounded in explicit policy would absolutely be something I'd weigh heavily in a competitive market for labor.
I really like the idea, though. I would love to get an extra paycheck at the end of the year.